1. Technical Field
The present invention is directed to a new method for the preparation of primary arsines from arsonic acids, particularly to the preparation of aliphatic arsines from aliphatic arsonic acids.
2. Brief Description of Background Art
Presently, arsine gas (having a boiling point of -62.5.degree. C.) is used in the semiconductor industry, for example, in the fabrication of gallium arsenide for use in making various high speed electronic devices and for use as a dopant in HgCdTe technology. It will be readily appreciated that the degree of purity of starting materials for use in such technological applications is highly important if not critical.
Arsine gas is highly toxic, the TLV in air of AsH.sub.3 being 0.05 parts per million (ppm). Thus it requires special precautions in handling. It would be desirable to find a less volatile and less toxic substitute of high purity for arsine gas.
The present inventors considered utilizing primary arsines containing a hydrocarbyl group, particularly an aliphatic hydrocarbyl group directly bonded to the arsenic atom, As, as substitutes for arsine gas. However, it is very difficult to make highly pure primary arsines from arsonic acids without involving multiple, highly labor intensive, purification steps involving the arsonic acid intermediates.
As discussed by A. J. Quick and R. Adams (hereinafter "Quick and Adams") in "Aliphatic Arsonic And Arsinic Acids, And Aliphatic-Aromatic Arsinic Acids", Journal of the American Chemical Society 44, 805-816 (1922), the lack of a satisfactory method of preparation of arsonic acids has inhibited development of compounds from arsonic acids (page 806). Of all methods available for preparing primary arsenic compounds, only the Meyer reaction, has any great importance. The Meyer reaction consists in the treatment of sodium arsenite with an alkyl halide to give an arsonic acid.
Quick and Adams disclose that in the Meyer reaction the alkyl halide probably reacts with the tautomeric forms of the sodium arsenite (Na.sub.2 O.sub.3 AsNa) producing compounds with the alkyl radical attached to arsenic as summarized by the following equation: ##STR1##
At pages 806-807, Quick and Adams report that historically the procedure for making arsonic acids was tedious, and it was difficult to get rid of the "impurities" for "isolation of the product". At page 807, Quick and Adams discuss some improvements on the Meyer synthesis of arsonic acids. However, even with the improvements discussed therein, the reference teaches that for isolation of the arsonic acid it is necessary to concentrate the solution, filter off the sodium halide (an impurity) and acidify. For example, the concentration step itself is still tedious and labor intensive and accordingly not suitable for large scale production.
Page 809 describes a general procedure for making an arsonic acid from arsenious oxide, sodium hydroxide solution, an alkyl halide and hydrochloric acid (for acidification). Page 810 describes a more specific procedure for making ethyl arsonic acid, C.sub.2 H.sub.5 As(O)(OH).sub.2. As can be appreciated from the preparation of ethyl arsonic acid described therein, the procedure involves multiple concentration and filtration steps after which a quantity as specified of "needle-like crystals" separates, together with a small quantity of sodium chloride (an impurity).
The article, "Aliphatic Chloroarsines" by C. K. Banks, J. F. Morgan et al, Journal of the American Chemical Society 69, 927-930 (1947), generally is directed to the reaction of alkyl halides with sodium arsenite or sodium alkyl arsenites to yield alkylarsonic and dialkylarsinic acids with subsequent reduction of these products with sulfur dioxide in the presence of hydrochloric acid to yield the corresponding alkyldichloro- and dialkylchloroarsines.
The article, "Primary Arsines" by W. M. Dehn, American Chemical Journal 33, 101-153, (1905), at page 103 discloses a general method for preparing primary and secondary arsines. The article generally discloses that mono- and dialkyl arsenic acids of the types: R.sub.2 AsOOH and RAsO(OH).sub.2 reduce by means of zinc and hydrochloric acid to secondary and primary arsines respectively. It also generally discloses that the reduction can be conducted using aromatic arsenic acids and specifically discloses that phenyl arsonic acid can be so reduced to produce monophenyl arsine.
U.S. Pat. No. 4,900,855 to Hui et al is directed to a method for providing highly pure mono- and dialkylarsines, particularly removing substantially all silicon-containing impurities therefrom, involving reaction of a monoalkylarsine or a dialkylarsine with either an alkali metal or an alkali metal hydrocarbyl thereby producing a solid alkali mono- or dialkylarsenide from which metal impurities can be removed by washing with appropriate solvent and/or drying in vacuo. The mono- or dialkylarsine may then be regenerated with a proton donor such as an acid, an alcohol or water.